Detection of anti-correlated hard X-ray time lag in Cygnus X-3

Abstract

The wide-band X-ray spectra of the high mass X-ray binary Cygnus X-3 exhibits a pivoting behavior in the `low' (as well as `hard') state, correlated to the radio emission. The time scale of the soft and hard X-rays' anti-correlation, which gave rise to the pivoting feature, was found to be less than a day from the monitoring observations by RXTE--ASM and CGRO--BATSE. In this Letter we report the detection of a lag of $\lesssim$ 1000s in the anti-correlation of the hard X-ray emission (20--50 keV) to that of the soft X-ray emission (2--7 keV), which may be attributed to the viscous time scale of flow of matter in the accretion disk. This suggests the geometrical picture of a truncated accretion disc with a Compton cloud inside the disc, the relative sizes of which determine the spectral shape. Any change in the disc structure will take place in a viscous time scale, with corresponding anti-correlated change in the Compton cloud. We also report the pivoting in the spectra in one span of a pointed observation when an episode of the rearranging of the accretion system is serendipitously observed. This is the first such observation of hard X-ray delay seen in the persistent Galactic microquasars, within the precincts of the hard state.

arXiv commentAccepted in The Astrophysical Journal (Letters): in press

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• Anti-correlated hard X-ray time lags in Galactic black hole sources
• Anti-correlated hard X-ray time lag in GRS 1915+105: evidence for a truncated accretion disc
• X-ray timing analysis of Cyg X-3 using AstroSat/LAXPC: Detection of milli-hertz quasi-periodic oscillations during the flaring hard X-ray state
• A precise measurement of the orbital period parameters of Cygnus X-3
• Evolution of cross-correlation and time lag of 4U 1735-44 along the branches
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• A truncated accretion disk in the galactic black hole source H1743-322
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• Cross-correlations between soft and hard light curves depending on luminosity in the transient neutron star XTE J1701-462
• The cross-correlation analysis in Z source GX 349+2
• Investigating the coronal structure by studying time lags in the Atoll source 4U 1705-44 using AstroSat
• A study of the cross-correlation and time lag in black hole X-ray binary XTE J1859+226